Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -19021,8 +19021,10 @@
                                     SDValue PreservedSrc,
                                     const X86Subtarget &Subtarget,
                                     SelectionDAG &DAG) {
-  if (isAllOnesConstant(Mask))
-    return Op;
+
+  if (auto *MaskConst = dyn_cast<ConstantSDNode>(Mask))
+    if (MaskConst->getZExtValue() & 0x1)
+      return Op;
 
   MVT VT = Op.getSimpleValueType();
   SDLoc dl(Op);
Index: test/CodeGen/X86/avx512-scalar_mask.ll
===================================================================
--- test/CodeGen/X86/avx512-scalar_mask.ll
+++ test/CodeGen/X86/avx512-scalar_mask.ll
@@ -26,6 +26,7 @@
   ret < 4 x float> %res
 }
 
+; FIXME: we should just return %xmm0 here.
 define <4 x float>@test_const0_mask(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const0_mask:
 ; CHECK:       ## BB#0:
@@ -36,6 +37,7 @@
   ret < 4 x float> %res
 }
 
+; FIXME: we should zero the lower element of xmm0 and return it.
 define <4 x float>@test_const0_maskz(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const0_maskz:
 ; CHECK:       ## BB#0:
@@ -46,6 +48,7 @@
   ret < 4 x float> %res
 }
 
+; FIXME: we should just return %xmm0 here.
 define <4 x float>@test_const2_mask(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const2_mask:
 ; CHECK:       ## BB#0:
@@ -56,6 +59,7 @@
   ret < 4 x float> %res
 }
 
+; FIXME: we should zero the lower element of xmm0 and return it.
 define <4 x float>@test_const2_maskz(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const2_maskz:
 ; CHECK:       ## BB#0:
@@ -87,9 +91,7 @@
 define <4 x float>@test_const_3_mask(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const_3_mask:
 ; CHECK:       ## BB#0:
-; CHECK-NEXT:    kxnorw %k0, %k0, %k0
-; CHECK-NEXT:    kshiftrw $15, %k0, %k1
-; CHECK-NEXT:    vfmadd213ss %xmm2, %xmm1, %xmm0 {%k1}
+; CHECK-NEXT:    vfmadd213ss %xmm2, %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %res = call <4 x float> @llvm.x86.avx512.mask.vfmadd.ss(<4 x float> %v0,<4 x float> %v1, <4 x float> %v2,  i8 3, i32 4)
   ret < 4 x float> %res
@@ -98,9 +100,7 @@
 define <4 x float>@test_const_3_maskz(<4 x float> %v0, <4 x float> %v1, <4 x float> %v2) {
 ; CHECK-LABEL: test_const_3_maskz:
 ; CHECK:       ## BB#0:
-; CHECK-NEXT:    kxnorw %k0, %k0, %k0
-; CHECK-NEXT:    kshiftrw $15, %k0, %k1
-; CHECK-NEXT:    vfmadd213ss %xmm2, %xmm1, %xmm0 {%k1} {z}
+; CHECK-NEXT:    vfmadd213ss %xmm2, %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %res = call <4 x float> @llvm.x86.avx512.maskz.vfmadd.ss(<4 x float> %v0,<4 x float> %v1, <4 x float> %v2,  i8 3, i32 4)
   ret < 4 x float> %res